Summary

Just as evolutionary biologists now know that similarities in form and function are no guarantee that distinct species are actually related, cell biologists are finding the same is true about cells. And just as evolutionary biologists now look to the DNA of organisms to understand their relationships, cell biologists should classify cells genetically as well, a small group of researchers now argues. Because each cell in an organism has the same set of genes, however, the idea is to instead use each cell type's distinctive pattern of gene activity. That approach has revealed that neurons in a variety of animals have two sources—from the tip of the embryo and from what becomes the animal's trunk, suggesting independent evolutionary origins as well. This approach is helping clarify the nature and origin of specialized cells in the mammalian uterus called decidual cells and, ultimately, has broad explanatory power.